Page 1 of 2 12 LastLast
Results 1 to 10 of 16

Thread: Is there something magical in correcting an '08 Corvette speedometer calibration???

  1. #1
    New Member
    Join Date
    Aug 2010
    Posts
    6

    Default Is there something magical in correcting an '08 Corvette speedometer calibration???

    I sent my '08 Vette ECM (6 speed manual) to a very well known and respected tuner who has tried twice now to get my C6 speedometer to read 2.5% slower than what it's currently reading (stock calibration) to compensate for my 305/30/19 rear tires...doesn't seem too tough, right?

    Well, I sent my ECM to this well known tuner to have their mail order tune done and have the speedometer calibrated. I gave him my tire size along with the other mods. Well, I get the ECM back, install it and take it for a ride. Low and behold I'm still off the IDENTICAL 2.5% I was before. I call them and he looks up my file and it shows that he did change it to my new tire size, but for whatever reason it didn't work. He told me to send it back to him and he will input it manually and that I have to just get him the speed I am actually going as well as the speed the speedometer thinks I am going. I do this and send the ECM back. He does this and sends it back to me once again. I just got back from taking it for a ride after the second try and it's -STILL- off the same exact amount it was before. Whatever is being changed is not doing a thing. What is the magic combination of check boxes and numbers in order to change a late model C6 speedometer calibration?

    So, with my current wheels/tires installed, running the stock calibration = 2.5% fast, first attempt at changing the calibration = 2.5% fast, second attempt = 2.5% fast. If I were to put my stock wheels back on the speedometer would once again be accurate. Whatever is getting changed isn't affecting my speedometer reading.

    All speeds were monitored using the same GPS in all three comparisons on the same stretch of FLAT road.

    Any help would be greatly appreciated!
    Paul
    Last edited by JRHAWK9; August 28th, 2010 at 02:07 AM.

  2. #2
    R.I.P Shawn, 1956-2011 WeathermanShawn's Avatar
    Join Date
    Jul 2008
    Posts
    1,807

    Default

    I have always used the 'Speedo Calculator' provided in the EFILive Tune Tool. I believe your year has one included. That calculates a new VSS that should match your actual speed.

    Its tough to get it completely accurate when you change tire size. Plus I believe your tire size changes at various speeds and loads. I also compare with GPS. I try to get it within 1-2 mph, with the speedo reading a little high (speed limit laws, etc..).

    If you don't have access to the 'Calculator', I am sure someone could run the numbers for you. There are quite a number of variables, so you might review them if you need to re-post.

    Good luck..
    2002 Black Camaro Z-28 M6 Hardtop 11.0:1CR 425HP/410TQ SAE (400TQ@3500RPM)
    200cc Heads, 228/232 110+2 Cam, 1 3/4" LT's w/catts, GMMG, Koni Shocks, Hotchkis Springs, 35/21 Sways, 17" ZR1's, 3.90 Gears Roadrunner PCM LM-2 Serial Wideband
    EFILive Closed-Loop MAF/SD Hybrid Tune..


  3. #3
    New Member
    Join Date
    Aug 2010
    Posts
    6

    Default

    that's essentially what I am doing when driving 100mph (as indicated by the speedometer) and comparing it to the GPS speed (which, in my case, reads right around 97.5 mph, +/- 0.1mph).

    Which, according to -HERE- and -HERE- is exactly what they should be off.


    Regardless of the math involved, my calibration hasn't changed a bit from the stock calibration in two attempts of trying to change it. This leads me to believe something isn't being changed in EFI Live that should be getting changed. Now if his changes were actually showing up in my speedometer readings, then we know the changes are actually taking and then we could discuss the math involved in dialing in accurate speedometer readings. At this point I would just like to see ANY kind of change to what what speedometer reads...lol If it goes from reading 2.5% too fast to reading 1% too slow at least we know whatever's being changed in EFI Live is actually working.

  4. #4
    R.I.P Shawn, 1956-2011 WeathermanShawn's Avatar
    Join Date
    Jul 2008
    Posts
    1,807

    Default

    I take it you are going through a Vendor, or do you have EFILive?

    If you do not, then I would download a tune from their site (for your year) and attempt to duplicate the necessary changes. You won't be able to flash a new tune, but at least you will have more information than you do now.

    Good luck..
    2002 Black Camaro Z-28 M6 Hardtop 11.0:1CR 425HP/410TQ SAE (400TQ@3500RPM)
    200cc Heads, 228/232 110+2 Cam, 1 3/4" LT's w/catts, GMMG, Koni Shocks, Hotchkis Springs, 35/21 Sways, 17" ZR1's, 3.90 Gears Roadrunner PCM LM-2 Serial Wideband
    EFILive Closed-Loop MAF/SD Hybrid Tune..


  5. #5
    New Member
    Join Date
    Aug 2010
    Posts
    6

    Default

    I am going through a vendor, correct. I guess I would rather have the vendor I am using know how to do this than me, as it's useless for me seeing I can't flash it to see what works and what doesn't.

    Where can I get this tune you are referring to? I could try installing EFI Live and opening up a tune and check out what's all involved.

  6. #6
    Joe (Moderator) joecar's Avatar
    Join Date
    Apr 2003
    Posts
    28,403

    Default

    What was your OEM tire size...?

    Your tire size is now 305/30R19...?

  7. #7
    New Member
    Join Date
    Aug 2010
    Posts
    6

    Default

    OEM was 285/35/19, I am now running a 305/30/19.

  8. #8
    R.I.P Shawn, 1956-2011 WeathermanShawn's Avatar
    Join Date
    Jul 2008
    Posts
    1,807

    Default

    I take it that is not a standard 'Plus Size'? I.E., its a different Tire Diameter than OEM?

    If that is the case, it can be tough fine-tuning a speedo. I would imagine the actual tire diameter being utilized in the VSS calculation is off. You can manipulate the speedo in EFILive and get close, but you almost need the program to do it right.

    I spent a month on mine, and I am happy getting it within 1-2 mph. It is all in the tire diameter. At 40 mph you can nail the speedo reading, and then it is off at 20 mph and/or 100 mph.

    I think it would get frustrating to keep sending an ECM out for such a small tweak. Sounds like it is time to get EFILive..
    2002 Black Camaro Z-28 M6 Hardtop 11.0:1CR 425HP/410TQ SAE (400TQ@3500RPM)
    200cc Heads, 228/232 110+2 Cam, 1 3/4" LT's w/catts, GMMG, Koni Shocks, Hotchkis Springs, 35/21 Sways, 17" ZR1's, 3.90 Gears Roadrunner PCM LM-2 Serial Wideband
    EFILive Closed-Loop MAF/SD Hybrid Tune..


  9. #9
    Lifetime Member
    Join Date
    Nov 2007
    Posts
    631

    Default

    No offense Paul, but is this post really about 2.5% ?? I mean I would consider that a good "safety margin" not
    to get a ticket but at 100 I don't think you are worried about that.
    I'm sure you have a nice car hell it's an 08 Vette !! At 100 you still have 90 mph left !!
    Focus on DRIVING, don't kill anyone or yourself and have fun with the car !!

  10. #10
    New Member
    Join Date
    Aug 2010
    Posts
    6

    Default

    what I am trying to get at is that any changes being made, regardless of the amount, should actually be showing up. In my case it wouldn't matter if it was off 25% or 2.5%, as the changes being made are not showing up. It's a CONSISTENT 2.5% it's off no matter what is "changed" in EFI Live. This tells me that the changes being made are not affecting the calibration in any way, shape or form. It just seems like something is not being changed in EFI that should be changed in order to apply the changes.

    I have an '00 Firehawk with different gears -AND- different sized tires and I never had any issues with getting that speedometer correctly calibrated.

Page 1 of 2 12 LastLast

Similar Threads

  1. Will E38 from 08 Corvette work in 2007 Corvette?
    By Chalky in forum Gen IV V8 Specific
    Replies: 2
    Last Post: June 5th, 2010, 09:00 AM
  2. Speedo correcting healp
    By Sixes350 in forum General (Petrol, Gas, Ethanol)
    Replies: 2
    Last Post: December 11th, 2009, 02:36 PM
  3. Correcting MAF Flow issue
    By Cougar281 in forum Diesel
    Replies: 4
    Last Post: March 19th, 2008, 01:26 PM
  4. Replies: 3
    Last Post: September 23rd, 2007, 05:01 AM
  5. Speedometer Calibration
    By TurboBeagleBuggy in forum General (Diesel)
    Replies: 6
    Last Post: January 6th, 2006, 07:28 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •